John stone stone



Patented Apr. 25,' I899.

J. S. STONE, DIFFERENTIAL ELEGTROIIAGNET.

(Application filed Aug. 6, 1898.)

(No Model.)

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UNITED STATES PATENT OFFICE,

JOHN STONE STONE, OF BOSTON, MASSACHUSETTS, ASSIGNOR TO THE AMERICAN BELL TELEPHONE COMPANY, OF SAME PLACE.

DIFFERENTIAHELEOTROMAAGNET.

SPECIFICATION forming part of Letters Patent No. 623,579, dated April 25, 1899.

Application filed August 6, 1898. Serial No. 687,902. (No model.)

To aZZ whom it may concern: structing such adouble-wound ditterentially- Be it known that 1, JOHN STONE STONE, reconnected electromagnet so that it shall have siding at Boston, in the county of Suifolk and no appreciable magnetic leakage between the State oflliassachusetts,haveinvented certain windings the core will in general be ener- 5 Improvements in Diiterential Electroinaggized by the passage of either constant or pulnets, of which the following is a specification. satory direct, or slowly-alternating currents,

In the operation of telephone-exchange or whereas the clectromagnet will offer but a other telephonic installations it is frequently relatively slight impedance to the passage of desirable to employ electromagnetic appararapidly=alternating currents. Moreover, I

1o tus connected in circuits through which curfind that such impedance asis oitered by the rents of diverse character-as, for instance, magnet when placed in a telephone-circuit to voicecurrents and signaling-currents ofposthe passage of telephone-currents is the same sibly several kinds-may circulate, and when for each of the simple components constitutthis is done it is obvious that for satisfactory ing the complex telephone-current, and for 15 results any such appliance must not only be this reason such a coil will not, when placed perfectly responsive to the current intended in a telephone-circuit, distort the telephonefor its operation, but also should be irresponcurrents which may circulate through it. sive to other currents, without impeding their This essential condition of no magnetic leakflow through their appropriate conductors age is to be obtained byso disposing the wind 20 and without distorting such telephonic or ings on the core that all, or substantially all, voice currents as may be required to pass theinduction developed byacurrentin either through its coils. winding passes through, is included in, or is Where in telephonic practice signaling or surrounded by the other winding, a condiother electromagnetic appliances are to be tion which may be more precisely stated by 25 employed possessing the severalrequirements saying that the mutual inductance between or characteristics of responsiveness to direct the two windings shall equal, or nearlyequaljkr constant, direct intermittent, or pulsatory or the square root of the product of the inductslowly-alternating currents, irresponsiveness ances of the windings.

to rapidly-alternating currents, low impe- In the foregoing statement that a double- 8o 0 dance to rapidly-alternating' currents, and wound eleetromagnet with its two windings little or no power of distorting or tending to connected or wound oppositely in parallel and distort the telephonecurrents which pass so constructed as to have no appreciable magthrough them, it is distinctly an advantage netic leakage between the windings will in to provide that their electromagnets shall be general have its core magnetized or excited 5 double wound and shall have their two Windby-the passage of a direct current through ings connected in parallel and differentially the windings the qualification in general or in reciprocal magnetic opposition, the is made necessary by the fact that if the ratio whole being constructed orarranged on a pebetween the number of turns and the resistculiar plan in conformity with principles to ance of the two windings, respectively, be the 0 v 4.0 be stated herein. I have found that it the same for both then obviously no magnetizatwo windings of such an electromagnet are so tion will result, even in the case of direct and relatively disposed upon thev iron magnetconstant currents, or we may say that if the core that there is no appreciable magnetic two windings had each the same number of leakage between the windings the said magturns and also the same resistance, so that 5 45 net-core will in general be excited by, the paswhen conducting current the ampere-turns sage through the windings of a direct current, in each would be the same, the iron core obvieither constant or pulsatory, or of a slowlyously would remain unexcited. Its armature alternating current, whereas it will not be would therefore remain unattracted, and any sensibly magnetized by the passage of a rapelectromagnetic apparatus or device depend- 50 idly-alternating current through the wind ing for its operation on the attraction of such ings. I have also discovered that by con armature would thus beirresponsiwe even to direct and constant currents. It follows from these considerations that besides the condition that the magnetic leakage of these double-wound and differentially-connectcd electromagnctic coils shall be zero it is necessary, in order that they shall be energized by or be responsive to constant or pulsatory direct currents or slowly-alternating currents, that the ratio of the number of turns to the resistance of each winding shall be different. This condition may be more precisely stated by saying that the time-constants of the two windings must be different. One practical way of carrying out these principles or conditions is to so construct the electromagnet that its two insulated conductor-windings shall have exactly the same number of turns, while the resistance of one shall be considerably greater than that of the other. The counter electromotive force of self-induction developed in an eleetromagnet so constructed on the passage of a rapidly-alternating cur rent is small, and the impedance offered by it to such currents therefore is also small, and since the relatively weak magnetizing power of either winding produced by the passage through it of a rapidly-alternating current is checked and further minimized by the opposed magnetizing power of the other under the simultaneous passage through it of the same current the resultant effect is so small that the electromagnet is not sensibly excited and is to such a current irresponsive; but a constant or pulsatory direct or a slowlyalternating current will. substantially divide between the two windings of diverse resistance inversely as their resistances, and as a consequence a resultant magnetizing effect upon the iron core will be produced, which with a current of appropriate strength will cause the attraction of the armature. This difference in resistance between the windings may be attained either by varying the size of the wires, by employing for the wires, respectively, metals of different resistivity, or by a combination of both cxpedients.

In the drawings which accompany and illustrate this specification, Figures 1 and 2 are respectively a longitudinal vertical section and a rear elevation of an electromagnetic relay embodying my invention. Fig. is a diagram representing the parallel, but magnetically-opposed, connection of two windings of diverse resistance on the same magnetic core; and Fig. T represents the connection of the relay shown in Fig. 1 wound, as in Fig. 3, in a telephone trunk-circuit where the requirements are as hereinbefore set forth.

1- indicates the electromagnetic signal or relay, secured to a suitable base 13. O is its iron core; a, its armature; D, an iron casing within which it is secured, and E the cappiece orarmature-chamber, furnished with an insulated back-stop or limit-screw s.

W and W are the two windings, each havin g the same number of turns, the resistances, however, being unlike, that of being considerably greater than that of \V.

In an electromagnetic signaling-relay constructed to embody this invention and put in operation and wherewith good results have been attained one of the two windings, each having three thousand six hundred and sixty turns, was of wire of .0126 of an inch diameter, while the diameter of the other was .0100 of an inch.

In Fig. at, H represents a trunk-circuit connection between two switchboards,which may be at different central stations X and Z, and is shown as being terminated at one of the said stations in a plug-socket or spring-jack J and at the other in a connecting-plug l. L is a loop extending from the said trunk and containing in one of its conductors the double-wound signaling-relay R. The relay has its two windings \V and XV diagrammatically shown as surrounding its iron core C, and its armature a controls a local signalingcireuit c, which includes, in addition to its battery, any suitable visual signal 2', as a selfsetting annunciator or aglow-lamp. lVhen the armature is attracted on the magnetic excitement of the core, it brings into contact the two terminals 1) (Z of the local circuit, and thus causes the same to operate the signal.

In constructing an electromagnetic appliance such as the doublewound relay described herein it is desirable to place that one of the two windings which has the lower resistance nearest to the iron core, inorder that the difference in resistance of the windings may be made as great as possible by taking advantage of the fact that, other things being equal, the resistance per convolution of wire increases with the radius.

I claim as my invention 1. An electromagnet or electromagnetic coil having two windings of different time-constants; connected in parallel; in opposition to each other; and substantially without magnetic leakage between them, as set forth.

2. The combination in an electromagnetic coil and with the iron core thereof; of two exciting-helices having substantially the same number of turns, but of unequal resistance, wound in parallel, and connected magneticallyor inductivelyin opposition upon the said iron core; and substantially without magnetic leakage between them; as set forth.

Intestimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, this 1st day of August, 1898.

JOHN STONE STONE.

\Vitnesses:

GEO. WILLIs PIERCE, FRANK C. LocKwooD.

ITO 

